Supramolecular-structured hydrogels showing a reversible phase transition by inclusion complexation between poly(ethylene glycol) grafted dextran andalpha-cyclodextrin

Supramolecular-structured hydrogels were prepared on basis of the inclusion complexation between poly(ethylene glycol) grafted dextrans and alpha-cycl odextrins (alpha -CDs) in aqueous media. The inclusion complexes from the P EG grafted dextrans showed a unique gel-sol phase transition which cannot b e obtained from usual polymer inclusion complexes that form crystalline pre cipitates. The gel-sol transition was based on the supramolecular assembly and dissociation, and the transition was reversible with hysteresis. The tr ansition temperature was controllable by variation in the polymer concentra tion and the PEG content in the graft copolymers as well as the stoichiomet ric ratio between the guest and host molecules. The properties of the hydro gel were characterized by DSC, X-ray diffraction, and C-13 CP/MAS NMR. The X-ray diffraction data indicated that the gel contains a channel-type cryst alline structure, demonstrated by a strong reflection at 2 theta = 20 degre es (d = 4.44 Angstrom). It was confirmed from the DSC and C-13 CP/MAS NMR m easurements that all the PEG grafts participate in the complexation. A phas e-separated structure consisting of hydrophobic and channel-type crystallin e PEG inclusion complex domains and hydrated dextran matrices was suggested as the internal structure, which comprises the supramolecular-structured h ydrogel.